全文获取类型
收费全文 | 26305篇 |
免费 | 979篇 |
国内免费 | 732篇 |
专业分类
化学 | 8483篇 |
晶体学 | 337篇 |
力学 | 662篇 |
综合类 | 75篇 |
数学 | 9710篇 |
物理学 | 8749篇 |
出版年
2023年 | 112篇 |
2022年 | 254篇 |
2021年 | 205篇 |
2020年 | 224篇 |
2019年 | 560篇 |
2018年 | 379篇 |
2017年 | 357篇 |
2016年 | 262篇 |
2015年 | 231篇 |
2014年 | 324篇 |
2013年 | 1251篇 |
2012年 | 599篇 |
2011年 | 1137篇 |
2010年 | 670篇 |
2009年 | 990篇 |
2008年 | 1117篇 |
2007年 | 1111篇 |
2006年 | 1082篇 |
2005年 | 787篇 |
2004年 | 1184篇 |
2003年 | 1292篇 |
2002年 | 1932篇 |
2001年 | 1882篇 |
2000年 | 1703篇 |
1999年 | 1847篇 |
1998年 | 1596篇 |
1997年 | 956篇 |
1996年 | 510篇 |
1995年 | 283篇 |
1994年 | 266篇 |
1993年 | 144篇 |
1992年 | 131篇 |
1991年 | 100篇 |
1990年 | 184篇 |
1989年 | 165篇 |
1988年 | 117篇 |
1987年 | 97篇 |
1986年 | 139篇 |
1985年 | 195篇 |
1984年 | 184篇 |
1983年 | 77篇 |
1982年 | 147篇 |
1981年 | 246篇 |
1980年 | 238篇 |
1979年 | 116篇 |
1978年 | 176篇 |
1977年 | 108篇 |
1976年 | 79篇 |
1975年 | 83篇 |
1974年 | 76篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
971.
A simple, rapid and specific chemiluminescence (CL) method for the determination of glutathione has been developed. The method
is based on the enhanced CL of the reaction between Ru(phen)3
2+ (phen = 1,10-phenanthroline) and KMnO4 by glutathione in HCl medium. Under the optimum conditions, the response is linearly proportional to the concentration of
glutathione between 1.5 × 10−7 and 1.0 × 10−5 mol L−1. The dection limit for glutathione (5.8 × 10−8 mol L−1) is about 10 and 200 times better than those of the spectrophotometric method using Ellman regent and the Lucigenin – CL
method, respectively. The final procedure allows the determination of glutathione in human serum with recoveries of 92%–108%.
A satisfactory agreement was obtained with a mean relative difference of 2.5% compared to the HPLC method. 相似文献
972.
Kagan Kerman Yasutaka Morita Yuzuru Takamura Mehmet Ozsoz Eiichi Tamiya 《Analytica chimica acta》2004,510(2):169-174
The unique binding event between Escherichia coli single-stranded DNA binding protein (SSB) and single-stranded oligonucleotides conjugated to gold (Au) nanoparticles is utilized for the electrochemical detection of DNA hybridization. SSB was attached onto a self-assembled monolayer (SAM) of single-stranded oligonucleotide modified Au nanoparticle, and the resulting Au-tagged SSB was used as the hybridization label. Changes in the Au oxidation signal was monitored upon binding of Au tagged SSB to probe and hybrid on the electrode surface. The amplified oxidation signal of Au nanoparticles provided a detection limit of 2.17 pM target DNA, which can be applied to genetic diagnosis applications. This work presented here has important implications with regard to combining a biological binding event between a protein and DNA with a solid transducer and metal nanoparticles. 相似文献
973.
The decay rate of vinyl unsaturation in high-density polyethylenes irradiated at temperatures from about 310 to 450 K, changes significantly in the melting range up to the crystalline melting point as does free radical mobility and the polymer crystallinity. However, orienting the polymer, or slow cooling or quenching from the melt, prior to irradiation, do not alter the decay process or its rate, although they do alter the rate of increase of insoluble gel and of elastic modulus in the molten state. It is suggested that, below 340 K, the marked deviations from a first-order decay result from the limited mobility of polymeric free radicals in the crystalline phase and from scavenging, by vinyl groups, segregated into the amorphous phase, of radiolytic hydrogen atoms (H). In the melting range, the mobility of polymeric free radicals increases as the crystallinity decreases, reducing the importance of scavenging, so vinyl decay approximates more closely to a first-order relation. In the melt, the vinyl decay relation is not changed qualitatively by H atom scavenging, but the effective vinyl concentration is lower, so the decay rate drops sharply. 相似文献
974.
975.
Anna Rakowska Robert Filipek Krzysztof Sikorski Marek Danielewski Renata Bachorczyk 《Mikrochimica acta》2004,145(1-4):183-186
The interdiffusion process in thin and thick (500nm–60µm) Au–Ni layers deposited on different substrates is studied using the EDS technique. In-depth X-ray analysis based on the Pouchou and Pichoir method is applied for obtaining the concentration profiles in nanometre scale multi-layers. A theoretical analysis using the Darken method is employed for modelling interdiffusion in the Au–Ni system. Computer simulations, where intrinsic diffusivities of the Au and Ni are functions of composition, are presented and compared with experimental results. 相似文献
976.
Davor Margetić Ronlad N. Warrener Mirjana Eckert-Maksić Ivana Antol Zoran Glasovac 《Theoretical chemistry accounts》2003,109(4):182-189
DFT calculations of 7′–oxasesquinorbornenes and 7,7′-dioxasesquinorbornenes using the B3LYP/6–31G* method are reported.
All the investigated structures (syn- and anti- derivatives) showed significant non-planarity of the central double bond, with the exception of those anti-derivatives possessing symmetrical structures. The influence of the replacement of the methylene groups at position 7- of
the norbornene fragment with oxygen and the introduction of second and third (peripheral) double bonds and benzene rings on
the molecular and electronic structures of these molecules have also been investigated.
Received: 11 November 2002 / Accepted: 6 June 2002 /
Published online: 29 April 2003 相似文献
977.
978.
Vinzenz Bachler 《Theoretical chemistry accounts》1997,96(4):223-242
A straightforward procedure is proposed for expanding a molecular orbital determinantal wave function into a set of determinantal
wave functions composed of atomic orbitals localized at the atoms of a molecule. By employing this method, atomic orbital
determinants and their weights can be derived for a molecule from the computed molecular-orbital wave function. The procedure
permits the interpretation of a molecular orbital determinantal wave function in terms of bonding schemes related to the classic
resonance structures used by organic chemists. By using the unrestricted molecular orbital determinant, bonding schemes and
their weights are obtained for butadiene, the butadiene radical cation and the acrylonitrile radical anion. Their dominant
bonding schemes are in accord with the relevant resonance structures for these molecules. For the butadiene radical cation
and the acrylonitrile anion they are shown to be compatible with the accepted mechanisms of the electrochemical coupling reactions
of butadiene and acrylonitrile.
Received: 7 August 1996 / Accepted: 18 March 1997 相似文献
979.
A very simple, selective and sensitive spectrophotometric method for the determination of dodecyl benzene sulfonate (DBS) has been investigated. In this method, the ion pair of DBS and methylene blue was adsorbed onto plasticized poly(vinylchloride) membrane as a solid phase extraction medium. The absorbance of the blue membrane was measured at 660nm against a blank membrane using a spectrophotometer. The influence of type and amount of plasticizer, pH, concentration of methylene blue, temperature of sample solution and time of extraction on the absorbance of membrane was studied. Linear calibration was obtained over a concentration range of 0.1 to 6.5µgmL–1 of DBS. The method was applied to the determination of DBS in different commercial detergents. The precision and accuracy of the method is comparable with the conventional standard method. This method is cost-effective, and the use of organic solvent such as chloroform is completely eliminated. 相似文献
980.
Analysis of Toxic Aluminium Species in Natural Waters 总被引:1,自引:0,他引:1
Gerlinde?WauerEmail author Hans-Jürgen?Heckemann Rainer?Koschel 《Mikrochimica acta》2004,146(2):149-154
Aluminium is known to be toxic to a wide range of aquatic organisms under certain conditions. Monomeric hydroxy ions have been found to be primarily responsible for aluminium aquatic toxicity.A survey of aluminium toxicity and a brief discussion of speciation schemes are presented. The fast reaction of Al3+ with pyrocatechol violet (PCV) followed by spectrophotometric analysis is a frequently used method for aluminium speciation. By using a flow system, one obtains fairly exact and reproducible control of the reaction time, and as a result it provides a direct method of analysis for free aluminium (including inorganic monomeric aluminium).The PCV-method has been adapted for the determination of aluminium in carbonate-rich natural waters using an improved buffering system. Thus it is possible to monitor aluminium concentrations in lake water as well as in pore water of the sediments of eutrophicated hardwater lakes that has been treated with aluminium salts as a restoration measure. 相似文献